Washington: The most striking photographs from Ferguson, Missouri, aren't of Saturday's demonstrations or Sunday night's riots; they're of the police. Image after image shows officers clad in Kevlar vests, helmets, and camouflage, armed with pistols, shotguns, automatic rifles, and tear gas. In one photo, protesters stand toe-to-toe with baton-wielding riot police, in another, an unarmed man faces several cops, each with rifles at the ready.

What's more, Ferguson police have used armoured vehicles to show force and control crowds. In one photo, riot gear-clad officers are standing in front of a mine-resistant ambush protected vehicle, barking commands and launching tear gas into groups of demonstrators and journalists.

This would be one thing if Ferguson were in a war zone, or if protesters were violent – although, it's hard to imagine a situation in which American police would need a mine-resistant vehicle. But an episode of looting aside, Ferguson police aren't dealing with any particular danger. Nonetheless, they're treating demonstrators – and Ferguson residents writ large – as a population to occupy, not citizens to protect.

In his book The Rise of the Warrior Cop, journalist Radley Balko notes that since the 1960s, "law-enforcement agencies across the US, at every level of government, have been blurring the line between police officer and soldier. Driven by martial rhetoric and the availability of military-style equipment – from bayonets and M-16 rifles to armoured personnel carriers – American police forces have often adopted a mind-set previously reserved for the battlefield."

This process ramped up with the "war on drugs" in the 1980s and 1990s, as the federal government supplied local and state police forces with military-grade weaponry to clamp down on drug trafficking and other crime. And it accelerated again after the September 11 attacks and the wars in Iraq and Afghanistan, when the federal government had – and sent – billions in surplus military equipment to state and local governments.

Police force protesters from the business district in Ferguson. Photo: AFP

Since 2006, according to an analysis by The New York Times, police departments have acquired 435 armoured vehicles, 533 planes, 93,763 machine guns and 432 mine-resistant armoured trucks.

Overall, since Congress established its program to transfer military hardware, local and state police departments have received $US4.3 billion worth of equipment. Accordingly, the value of military equipment used by these police agencies has increased from $US1 million in 1990 to $US324 million in 1995 (shortly after the program was established), to nearly $US450 million in 2013.

At the same time as crime has fallen to its lowest levels in decades, police departments are acquiring more hardware and finding more reasons to use SWAT teams and other heavy-handed tactics, regardless of the situation.

A protester takes shelter from a smoke bomb. Photo: AP

According to an American Civil Liberties Union report released this summer, 79 per cent of SWAT deployments from 2011 to 2012 were for search warrants, a massive overreaction that can have disastrous consequences, including injury and death.

That was the case for Aiyana Stanley-Jones, who was killed during a SWAT raid by the Detroit police department. Serving a search warrant for an occupant of the house, Detroit police rushed in with flash bangs and ballistic shields. When one resident tried to grab an officer's gun, it fired, striking Aiyana. She was seven.

If you know anything about the racial disparities in the US criminal justice system, then it also shouldn't shock you to learn that SWAT deployments are used disproportionately in black and Latino neighbourhoods. The ACLU found that 50 per cent of those affected by SWAT deployments were black and Latino. Of these deployments, 68 per cent were for drug searches.

That police are eager to use their new weapons and vehicles isn't a surprise. As The New York Times notes, "The ubiquity of SWAT teams has changed not only the way officers look, but also the way departments view themselves. Recruiting videos feature clips of officers storming into homes with smoke grenades and firing automatic weapons."

That is how we get images like the ones in Ferguson, where police officers brandish heavy weapons and act as an occupying force. We should expect as much when we give police departments military weapons. Already – when it comes to predominantly black and brown communities – there's a long-standing culture of aggressive, punitive policing. Add assault weapons and armoured vehicles, and you have a recipe for the repressive, violent reactions that we see in Ferguson, and that are likely inevitable in countless other poor American neighbourhoods.